The present invention relates to a material and method for making an electroconductive pattern.
For the fabrication of flexible LC displays, electrolumin-escent devices and photovoltaic cells transparent ITO (indium-tin oxide) electrodes are used. These electrodes are made by vacuum sputtering of ITO onto a substrate. This method involves high temperatures, up to 250xc2x0 C., and therefore glass substrates are generally used. The range of potential applications is limited, because of the high fabrication costs, the low flexibility (pliability) and stretchability as a consequence of the brittleness of the ITO layer and the glass substrate. Therefore the interest is growing in all-organic devices, comprising plastic resins as a substrate and organic electroconductive polymer layers as electrodes. Such plastic electronics allow the realization of low cost devices with new properties (Physics World, March 1999, p.25-39). Flexible plastic substrates can be provided with an electroconductive polymer layer by continuous roller coating methods (compared to batch process such as sputtering) and the resulting organic electrodes enable the fabrication of electronic devices characterised by a higher flexibility and a lower weight.
The production and the use of electroconductive polymers such as polypyrrole, polyaniline, polyacetylene, polyparaphenylene, polythiophene, polyphenylenevinylene, polythienylenevinylene and polyphenylenesulphide are known in the art.
EP-A 440 957 discloses dispersions of polythiophenes, constructed from structural units of formula (I): 
in which R1 and R2 independently of one another represent hydrogen or a C1-4-alkyl group or together form an optionally substituted C1-4-alkylene residue, in the presence of polyanions. Furthermore, EP-A-686 662 discloses mixtures of A) neutral polythiophenes with the repeating structural unit of formula (I), 
in which R1 and R2 independently of one another represent hydrogen or a C1-C4 alkyl group or together represent an optionally substituted C1-C4 alkylene residue, preferably an optionally with alkyl group substituted methylene, an optionally with C1-C12-alkyl or phenyl group substituted 1,2-ethylene residue or a 1,2-cyclohexene residue, and B) a di- or polyhydroxy- and/or carboxy groups or amide or lactam group containing organic compound; and conductive coatings therefrom which are tempered at elevated temperature, preferably between 100 and 250xc2x0 C., during preferably 1 to 90 seconds to increase their resistance preferably to  less than 300 ohm/square.
Coated layers of organic electroconductive polymers can be structured into patterns using known microlithography techniques. In WO-A-97 18944 a process is described wherein a positive or negative photoresist is applied on top of a coated layer of an organic electroconductive polymer, and after the steps of selectively exposing the photoresist to UV light, developing the photoresist, etching the electroconductive polymer layer and finally stripping the non-developed photoresist with an organic solvent, a patterned layer is obtained. A similar technique has been described in 1988 in Synthetic Metals, volume 22, pages 265-271 for the design of an all-organic thin-film transistor. Such methods are cumbersome as they involve many steps and require the use of hazardous chemicals.
EP-A 399 299 discloses a structure comprising: a polymeric material; the polymeric material being selected from the group consisting of substituted and unsubstituted polyparaphenylene-vinylenes, polyanilines, polyazines, polythiophenes, poly-p-phenylene sulfides, polyfuranes, polypyrroles, polyselenophenes, polyacetylenes formed from soluble precursors and combinations thereof and blends thereof with other polymers; preselected regions of the polymer material being electrically conductive; the conductive regions being substantially insoluble; and the remainder of the material being substantially soluble.
U.S. Pat. No. 5,427,841 discloses a laminated structure comprising an electrically insulating substrate carrying a polymer layer consisting essentially of a polymer selected from the group of poly(3,4-ethylenedioxythiophene, poly(3,4-diethylenedioxythiophene) wherein the ethylene group is substituted with C1-12 alkyl group, poly(3,4-ethylenedioxythiophene) wherein the ethylene group is substituted with an alkoxy group, and oligomers of ethylenedioxy-thiophene, the layer having a sheet resistance of maximally 1000 xcexa9/square, and a pattern of second substantially non-conductive portions whose sheet resistance is at least a factor of 106 higher than that of the conductive polymer in the first portions, a metal layer being deposited into the electrically conductive first portions of the polymer layer. In Exemplary embodiment 1 surface resistivity differentiation is realized by doping a poly(3,4-ethylenedioxythiophene)-containing layer with imidazole and pattern-wise exposure with UV-light (xcex less than 300 nm) by means of a mercury lamp.
It is an aspect of the present invention to provide a material having an outermost layer that can be processed to an electroconductive pattern by a simple, convenient method.
An electroconductive pattern can be realized with the materials of the present invention by pattern-wise exposure without removal of the unexposed or exposed areas, with or without a subsequent single wet processing step. No etching liquids or organic solvents are required.
The aspects of the present invention are realized by a material for making an electroconductive pattern, the material comprising a support and a light-exposure differentiable element, characterized in that the light-exposure differentiable element comprises a conductivity enhanced outermost layer containing a polyanion and a polymer or copolymer of a substituted or unsubstituted thiophene, and optionally a second layer contiguous with the outermost layer; and wherein the outermost layer and/or the optional second layer contains a monodiazonium salt capable upon exposure of reducing the conductivity of the exposed parts of the outermost layer relative to the unexposed parts of the outermost layer.
The aspects of the present invention are further realized by a material for making an electroconductive pattern, the material comprising a support and a light-exposure differentiable element, characterized in that the light-exposure differentiable element comprises an outermost layer having a surface resistance lower than 106 xcexa9/square containing a polyanion and a polymer or copolymer of a substituted or unsubstituted thiophene, and optionally a second layer contiguous with the outermost layer; and wherein the outermost layer and/or the optional second layer contains a monodiazonium salt capable upon exposure of reducing the conductivity of the exposed parts of the outermost layer relative to the unexposed parts of the outermost layer.
The aspects of the present invention are also realized by a method of making an electroconductive pattern on a support comprising the steps of:
providing a material for making an electroconductive pattern as in the two embodiments disclosed above; and
image-wise exposing the material thereby obtaining reduction in the conductivity of the exposed areas relative to non-exposed areas, optionally with a developer.
Further advantages and embodiments of the present invention will become apparent from the following description.
The term xe2x80x9csupportxe2x80x9d means a xe2x80x9cself-supporting materialxe2x80x9d so as to distinguish it from a xe2x80x9clayerxe2x80x9d which may be coated on a support, but which itself is not self-supporting. It also includes any treatment necessary for, or layer applied to aid, adhesion to the light-exposure differentiable element.
The term electroconductive means having a surface resistance below 106 xcexa9/square. Antistatic materials have surface resistances in the range from 106 to 1011 xcexa9/square and cannot be used as an electrode.
Conductivity enhancement refers to a process in which contact with high boiling point liquids such as di- or polyhydroxy- and/or carboxy groups or amide or lactam group containing organic compound optionally followed by heating at elevated temperature, preferably between 100 and 250xc2x0 C., during preferably 1 to 90 seconds, results in conductivity increase. Alternatively in the case of aprotic compounds with a dielectric constant xe2x89xa715, e.g. N-methyl-pyrrolidinone, temperatures below 100xc2x0 C. can be used. Such conductivity enhancement is observed with polythiophenes and can take place during preparation of the outermost layer or subsequently. Particularly preferred liquids for such treatment are N-methyl-pyrrolidinone and diethylene glycol such as disclosed in EP-A 686 662 and EP-A 1 003 179.
The term light-exposure differentiable element means an element which upon light exposure produces changes in the properties or composition of the exposed parts of the element with respect to the properties or composition of the unexposed parts of the element.
The term diazonium salt includes all compounds with two nitrogen atoms bonded together with a double or triple bond and includes xe2x80x94Nxe2x89xa1N+ and xe2x80x94Nxe2x95x90Nxe2x80x94R groups e.g. xe2x80x94Nxe2x95x90Nxe2x80x94SO3M groups.
The term surface resistance ratio between exposed and non-exposed areas means the ratio of the surface resistance of the exposed parts (areas) of the outermost layer to the unexposed parts (areas) of the outermost layer after optional processing.
The term xe2x80x9celectroconductivexe2x80x9d is related to the electric resistivity of the material. The electric resistance of a layer is generally expressed in terms of surface resistance Rs (unit xcexa9; often specified as xcexa9/square). Alternatively, the electroconductance may be expressed in terms of volume resistivity Rv=Rsxc2x7d, wherein d is the thickness of the layer, volume conductivity kv=1/Rv [unit: S(iemens)/cm] or surface conductance ks=1/Rs [unit: S(iemens).square].
All values of electric resistance presented herein are measured according to one of the following methods. In the first method the support coated with the electroconductive outermost layer is cut to obtain a strip having a length of 27.5 cm and a width of 35 mm and strip electrodes are applied over its width at a distance of 10 cm perpendicular to the edge of the strip. The electrodes are made of an electroconductive polymer, ECCOCOAT CC-2 available from Emerson and Cumming Speciality polymers. Over the electrode a constant potential is applied and the current flowing through the circuit is measured on a pico-amperometer KEITHLEY 485. From the potential and the current, taking into account the geometry of the area between the electrodes, the surface resistance in xcexa9/square is calculated.
In the second method, the surface resistance was measured by contacting the outermost layer with parallel copper electrodes each 35 mm long and 35 mm apart capable of forming line contacts, the electrodes being separated by a teflon insulator. This enables a direct measurement of the surface resistance.
Supports for use according to the present invention include polymeric films, silicon, ceramics, oxides, glass, polymeric film reinforced glass, glass/plastic laminates, metal/plastic laminates, paper and laminated paper, optionally treated, provided with a subbing layer or other adhesion promoting means to aid adhesion to the light-exposure differentiable element. Suitable polymeric films are poly(ethylene terephthalate), poly(ethylene naphthalate), polystyrene, polyethersulphone, polycarbonate, polyacrylate, polyamide, polyimides, cellulosetriacetate, polyolefins and polyvinylchloride, optionally treated by corona discharge or glow discharge or provided with a subbing layer.
A light-exposure differentiable element, according to the present invention, is an element which upon light exposure produces changes in the properties or composition of the exposed parts of the element with respect to the properties or composition of the unexposed parts of the element. According to the present invention, these changes in the properties or composition of the light-exposure differentiable element are due to the presence of a monodiazonium salt in the outermost layer and/or optional contiguous second layer, which upon exposure increases the surface resistance of the exposed areas. The optional second layer must be between the outermost layer and the support as it cannot be the outermost layer. Combinations of monodiazonium salt can also be used. Increasing the pH of the coating dispersions and solutions used in preparing the light-exposure differentiable element has been found to improve the shelf-life of materials according to the present invention. pH""s between 2.5 and 9 are preferred, with pH""s between 3 and 6 being particularly preferred. Such pH""s can, for example, be advantageously realized by adding ammonium hydroxide.
Polymer or Copolymer of a Substituted or Unsubstituted Thiophene
In a first embodiment of the material according to the present invention the polymer of a substituted or unsubstituted thiophene corresponds to the formula (I): 
in which n is larger than 1 and each of R1 and R2 independently represents hydrogen or an optionally substituted C1-4 alkyl group or together represent an optionally substituted C1-4 alkylene group or an optionally substituted cycloalkylene group, preferably an ethylene group, an optionally alkyl-substituted methylene group, an optionally C1-12 alkyl- or phenyl-substituted ethylene group, a 1,3-propylene group or a 1,2-cyclohexylene group.
The preparation of such a polythiophene and of aqueous dispersions containing such a polythiophene and a polyanion is described in EP-A-440 957 and corresponding US-P-5 300 575. Basically the preparation of polythiophene proceeds in the presence of polymeric polyanion compounds by oxidative polymerisation of 3,4-dialkoxythiophenes or 3,4-alkylenedioxythiophenes according to the following formula: 
wherein R1 and R2 are as defined above.
Stable aqueous polythiophene dispersions having a solids content of 0.05 to 55% by weight and preferably of 0.1 to 10% by weight can be obtained by dissolving thiophenes corresponding to the formula above, a polyacid and an oxidising agent in an organic solvent or preferably in water, optionally containing a certain amount of organic solvent, and then stirring the resulting solution or emulsion at 0xc2x0 C. to 100xc2x0 C. until the polymerisation reaction is completed. The polythiophenes formed by the oxidative polymerisation are positively charged, the location and number of such positive charges being not determinable with certainty and therefore not mentioned in the general formula of the repeating units of the polythiophene polymer.
The oxidising agents are those which are typically used for the oxidative polymerisation of pyrrole as described in for example J. Am. Soc. 85, 454 (1963). Preferred inexpensive and easy-to-handle oxidising agents are iron(III) salts, e.g. FeCl3, Fe(ClO4)3 and the iron(III) salts of organic acids and inorganic acids containing organic residues. Other suitable oxidising agents are H2O2, K2Cr2O7, alkali or ammonium persulphates, alkali perborates, potassium permanganate and copper salts such as copper tetrafluoroborate. Air or oxygen can also be used as oxidising agents. Theoretically, 2.25 equivalents of oxidising agent per mol of thiophene are required for the oxidative polymerisation thereof (J. Polym. Sci. Part A, Polymer Chemistry, Vol. 26, p.1287, 1988). In practice, however, the oxidising agent is used in excess, for example, in excess of 0.1 to 2 equivalents per mol of thiophene.
The polyacid forms a polyanion or, alternatively, the polyanion can be added as a salt of the corresponding polyacids, e.g. as an alkali salt. Preferred polyacids or salts thereof are polymeric carboxylic acids such as poly(acrylic acid), poly((meth)acrylic acid) and poly(maleic acid) or polymeric sulphonic acids such as poly(styrene sulphonic acid) or poly(vinyl sulphonic acid). Alternatively, copolymers of such carboxylic and/or sulphonic acids and of other polymerizable monomers such as styrene or acrylates can be used.
In a second embodiment of the material according to the present invention the polyanion is poly(styrene sulphonate).
The molecular weight of these polyanion forming polyacids is preferably between 1000 and 2xc3x97106, more preferably between 2000 and 5xc3x97105. These polyacids or their alkali salts are commercially available and can be prepared according to the known methods, e.g. as described in Houben-Weyl, Methoden der Organische Chemie, Bd. E20 Makromolekulare Stoffe, Teil 2, (1987), pp. 1141.
The coating dispersion or solution of a polyanion and a polymer or copolymer of a substituted or unsubstituted thiophene can also comprise additional ingredients, such as one or more binders, one or more surfactants, spacing particles, UV-filters or IR-absorbers.
Anionic and non-ionic surfactants are preferred. Suitable surfactants include ZONYL(trademark) FSN 100 and ZONYL(trademark) FSO 100, an ethoxylated non-ionic fluoro-surfactant with the structure: F(CF2CF2)yCH2CH2O(CH2CH2O)xH, where x=0 to ca. 15 and y=1 to ca. 7, both from Du Pont.
Suitable polymer binders are described in EP-A 564 911. Such binders may be treated with a hardening agent, e.g. an epoxysilane such as 3-glycidyloxypropyltrimethoxysilane as described in EP-A 564 911, which is especially suitable when coating on a glass substrate.
The coating dispersion or solution of a polyanion and a polymer or copolymer of a substituted or unsubstituted thiophene preferably also comprises an organic compound that is: a linear, branched or cyclic aliphatic C2-20 hydrocarbon or an optionally substituted aromatic C6-14 hydrocarbon or a pyran or a furan, the organic compound comprising at least two hydroxy groups or at least one xe2x80x94COX or xe2x80x94CONYZ group wherein X denotes xe2x80x94OH and Y and Z independently of one another represent H or alkyl; or a heterocyclic compound containing at least one lactam group. Examples of such organic compounds are e.g. N-methyl-2-pyrrolidinone, 2-pyrrolidinone, 1,3-dimethyl-2-imidazolidone, N,N,Nxe2x80x2,Nxe2x80x2-tetramethylurea, formamide, dimethylformamide, and N,N-dimethylacetamide. Preferred examples are sugar or sugar derivatives such as arabinose, saccharose, glucose, fructose and lactose, or di- or polyalcohols such as sorbitol, xylitol, mannitol, mannose, galactose, sorbose, gluconic acid, ethylene glycol, di- or tri(ethylene glycol), 1,1,1-trimethylol-propane, 1,3-propanediol, 1,5-pentanediol, 1,2,3-propantriol, 1,2,4-butantriol, 1,2,6-hexantriol, or aromatic di- or polyalcohols such as resorcinol.
In a third embodiment of the material according to the present invention the monodiazonium salts used in the present invention is a monoaryldiazoniumsulphonate salt.
In an fourth embodiment of the material according to the present invention the monodiazoniumsulphonate salt is represented by formula (II):
Arxe2x80x94Nxe2x95x90Nxe2x80x94SO3Mxe2x80x83xe2x80x83(II)
where Ar is a substituted or unsubstituted aryl group; and M is a cation. Ar preferably represents an unsubstituted phenyl group or a phenyl group substituted with one or more alkyl groups, substituted alkyl groups, aryl groups, alkoxy groups, aryloxy groups, amino groups or substituted amino groups, which may be linked with one another to form an alicylic or heterocyclic ring. M preferably represents a cation such as NH4+ or a metal ion such as a cation of Al, Cu, Zn, an alkaline earth metal or alkali metal.
Suitable monoaryldiazoniumsulphonate salts according to formula (II) are:
In a fifth embodiment of the material according to the present invention the monodiazonium salt is MADS01 or MADS06.
In the materials for making an electroconductive pattern, according to the present invention, the light-exposure differentiable element contains a binder.
In a sixth embodiment of the material according to the present invention the outermost layer contains a binder, e.g. polyvinyl alcohol and a hydroxyethyl methacrylate copolymer.
In a seventh embodiment of the material according to the present invention the optional second layer contains a binder, e.g. polyvinyl alcohol and a hydroxyethyl methacrylate copolymer.
Suitable binders for use in the present invention are described in EP-A 564 911 and include water-soluble polymers, such as poly(vinyl alcohol), water-soluble homo- and co-polymers of acrylic acid and homo- and co-polymers of methacrylic acid, and polymer latexes. Preferred binders include poly(vinyl alcohol) and homo- and co-polymers of hydroxyethyl methacrylate and copolymers of 2-propenoic acid 2-phosphonooxy)ethyl ester, copolymers of 2-methyl-2-propenoic acid 2-phosphonooxy)ethyl ester. Such binders may be treated with a hardening agent, e.g. an epoxysilane such as 3-glycidyloxypropyltrimethoxysilane as described in EP-A 564 911, which is especially suitable when coating on a glass substrate.
The material of the present invention can be image-wise exposed to ultraviolet light optionally in combination with blue light in the wavelength range of 250 to 500 nm or infrared light. Upon image-wise exposure, a differentiation of the surface resistance optionally with a developer of the exposed and non-exposed areas is induced. Useful exposure sources are high or medium pressure halogen mercury vapour lamps, e.g. of 1000 W or lasers having an emission wavelength in the range from about 700 to about 1500 nm, such as a semiconductor laser diode, a Nd:YAG or a Nd:YLF laser.
After the image-wise exposure the material is optionally rinsed in a developer, which can be plain water or is preferably water-based, to remove residual monodiazonium salt. During this rinsing process the outermost layer remains intact.